Growth and Survival of Postmetamorphic Toads: Interactions among Larval History, Density, and Parasitism

Abstract

I examined growth and survival of the European toad, Bufo bufo, from hatching to the approximate time of first hibernation. I varied tadpole density in experimental ponds such that individuals from low—density ponds emerged 48.5% larger than those from high—density ponds. In the laboratory, metamorphs from both pond densities were maintained in containers at densities of one or six. Nine weeks after metamorphosis they were exposed to 0 or 80 larvae of the lungworm, Rhabdias bufonis. A factorial experiment aimed to determine (1) the extent to which conditions experienced by larvae carried over to the terrestrial stage (2) the effects of resource limitation and past history on a host's response to a potential pathogen. The density of metamorphs had the strongest effect on growth and survival: 18 wk after metamorphosis, those raised alone were °80% heavier than those in groups and they had 31% higher survival. However, larval history also affected growth and survival and affected how metamorphs responded to density. First, single toads emerging from low—density ponds were 14.5% larger at the time of hibernation than those from high—density ponds. The mechanism for this growth advantage probably lies in the consistently higher growth rates of single toads from low—density ponds, especially during the first 3 wk after metamorphosis. Second, survival in group containers was higher for toads from low—density ponds, especially during the first few weeks after metamorphosis when most deaths involved toads from high—density ponds. These results support a carry—over effect between larval history and subsequent performance in an organism with a complex life cycle. Infection with lungworms had no detectable effect on metamorph growth or survival. This result contrasts earlier studies on this system, possibly due to the relatively low worm burdens or low statistical power. Yet, the results may also indicate that the predicted impact of infection on hosts, especially those limited by resources, is not as straightforward as theoretical studies suggest.